Ajax calls failing

Hi,
Recently I have updated my application from Uiwebview to wkwebview for that I have done following updates:

• Updated my ios platform to 5.1.1

• Added plugin cordova-plugin-wkwebview-engine

• Added plugin cordova-plugin-wkwebview-file-xhr

• Added <platform name="ios">

<preference name="WKWebViewOnly" value="true" />

Code Block 
<feature name="CDVWKWebViewEngine">
		<param name="ios-package" value="CDVWKWebViewEngine" />
</feature>

<preference name="CordovaWebViewEngine" value="CDVWKWebViewEngine" />
</platform>

but my ajax calls are failing in ios devices any suggestions